In U.S. Pat. No. 5,448,582, issued Sep. 5, 1995, entitled "Optical Sources Having a Strongly Scattering Gain Medium Providing Laser-Like Action", the inventor disclosed a multi-phase gain medium including an emission phase (such as dye molecules) and a scattering phase (such as TiO.sub.2). A third, matrix phase may also be provided in some embodiments. Suitable materials for the matrix phase include solvents, glasses and polymers. The gain medium is shown to provide a laser-like spectral linewidth collapse above a certain pump pulse energy. FIGS. 13a through 13f illustrate various embodiments of the invention wherein the gain medium is contained within or on a portion of an optical fiber or catheter for providing a desired wavelength at a localized region. Reference can also be had to FIGS. 10a and 10b, wherein a structure containing the gain medium is used to provide one or more wavelengths. The structure can be used to remove, by example, undesired skin pigments by providing electromagnetic radiation at a wavelength or wavelengths that are strongly absorbed by the pigment or pigments.
Photo-dynamic therapy (PDT) is a relatively new approach to treating many cancers. Patients are injected with one or more photo-sensitive drugs, such as one known as Photofrin, that bind to the rapidly dividing cells. A narrow-band laser is then used to excite the drugs, inducing a reaction which kills the cells. PDT has been used to treat esophageal cancer, Kaposi's sarcoma, an AIDS related condition, and the overgrowth of blood vessels in the eye (macular degeneration), which afflicts seven million people in North America alone.
One problem with current PDT techniques is that they require the use of expensive lasers to provide the various wavelengths required by current (and future) photosensitive drugs. The dye laser, because of its tunability, is often used for PDT applications. However, a typical dye laser can easily cost some tens of thousands of dollars. Also, the dye laser requires a complex assembly of tubing and pumps to inject a dye solution between precisely aligned mirrors. As such, the dye laser is not readily portable, and requires a significant amount of routine maintenance to remain in an operational condition. Furthermore, the dye laser requires a second laser to pump the dye solution.
As such, current PDT techniques require at least two lasers. For example, and referring to FIG. 1, a PDT excitation system 1 includes a Nd:YAG laser 2 that is used as a pump source (.lambda..sub.1) for a dye laser 3, from which the desired wavelength (.lambda..sub.2) of light is conducted, via a catheter 4 that contains an optical fiber, to the diseased tissue. The light is scattered on the tissue by a specially prepared tip that may include a scattering region 6 coupled to a mirror 5.